Soil Particulate Organic Matter Dynamics after Conservation Reserve Program Land Is Converted to Cropland.

The objective of this project is to compare the soil C quality in Conservation Reserve Program (CRP) vs. land under Sorghum cropping or rangeland in the Southern High Plains. Whole soils as well as light fraction particulate organic matter (lfPOM) was assessed using diffuse reflectance Fourier transformed mid infrared spectroscopy (DRIFTS) to identify the vegetation, depth and soil type effects on soil chemical quality. The DRIFTS was also used to determine is spectral data can be used to successfully predict the C and ¹³C content of whole soils and lfPOM. Our results show that the amount of lfPOM was lowest in the cropland soils relative to the rangeland. When the data was normalized according to silt+clay content, the SOC was rangeland=CRP>cropland.  The total POM content was rangeland>CRP>cropland. The POM from the CRP, however had low C concentration. While the whole soils from the CRP and crop had indistinguishable DRIFTS spectra. However, the DRIFTS data of the lfPOM was used to discern between the CRP and cropland due to the increased absorbance of clay and silicate minerals in the CRP samples. Partial Least Squares regression shows the potential of DRIFTS data to predict POM-C, with a calibration R2 of 0.67. Other data related to δ¹³C ratios in the POM and whole soils was poorly predicted. Our results show that the POM can be used as an early indicator of soil management change, and the infrared spectroscopy can be valuable to monitor changes in the mineral and organic composition of lfPOM.